glsl/parser: extract consts/exts/api out of context at start.

This stores these pointers separately. in theory now gl_context
can be made more opaque later, if we split header files ups.

Acked-by: Pierre-Eric Pelloux-Prayer <pierre-eric.pelloux-prayer@amd.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/14437>

src/compiler/glsl/ast_function.cpp

@@ -631,7 +631,7 @@ generate_call(exec_list *instructions, ir_function_signature *sig,
     * instructions; just generate an ir_constant.
     */
    if (state->is_version(120, 100) ||
-       state->ctx->Const.AllowGLSLBuiltinConstantExpression) {
+       state->consts->AllowGLSLBuiltinConstantExpression) {
       ir_constant *value = sig->constant_expression_value(ctx,
                                                           actual_parameters,
                                                           NULL);